Aided by good weather, Mexico produced a bumper crop of opium poppies last year. U.S. officials say the Mexican government has made major progress in the fight against illegal drugs. But drug cartels are responding by boosting cultivation and fighting eradication efforts.

A U.S. State Department report issued earlier this month says opium poppy cultivation In Mexico increased by 78 percent in 2003.

The report cites excellent weather conditions, but also observes that the narcotics cartels are planting more opium poppies. The report says marijuana cultivation also increased last year, by 70 percent.

The Mexican Attorney General's office says the government is determined to reduce the spread of drug crops, and fight those behind the cultivation, refining and international distribution.

The Attorney General's office reports a slight increase in the destruction of opium poppy and marijuana plantations nationwide by helicopters spraying herbicides. But cartels are responding by shooting at the pilots.

Professor Jorge Chabat is director of International Studies at the Center for Research, Technology and Economics in Mexico City. He specializes in research and analysis focusing on illegal narcotics. He says the increasingly aggressive tactics of the drug cartels show that Mexican authorities are succeeding in disrupting the cultivation phase, and cracking down on corruption among law enforcement authorities.

"The impression that I have, and you have some other indicators of that, especially in terms of arrests of big drug lords, is that, probably, the Mexican government is becoming more efficient, and corruption has been fought by this government," he said. "And that's why the drug traffickers are becoming more aggressive, because their business is being affected."

Mexican President Vicente Fox has made the fight against the drugs cartel his number one law and order priority.